Recently, emphasis has been placed on the development of membrane-type electrolytic cells for the production of alkalis and halogens, especially caustic and chlorine. This has come about primarily owing to the objections to the introduction of mercury and asbestos into the environment from the conventional chloralkali processes and is made possible because truly satisfactory membranes for such processes have only recently become available. However, due to previous inexperience with membrane cells for the electrolysis of alkali metal chloride except on a laboratory scale, unexpected problems have arisen in attempting to scale up prior technology to a commercial level.
For example, because these membranes swell considerably upon conversion from a dry to a wet state, it is desirable to install said membranes in a wet condition to avoid subsequent alterations in dimension. However, while maintaining small membranes in a wet condition presents no problems, handling of large, wet membranes is difficult and assembly is not always rapid enough to preclude drying of the membrane.
After installation of the membrane and assembly of the cell, it is essential that electrolysis be commenced rapidly to prevent the necessity for keeping an entire cell circuit closed down while waiting for one cell to come on line. However, even at high applied voltages, e.g., 10 volts or more, most cation-exchange membranes fail to pass significant amounts of current until they have become equilibrated, i.e., thoroughly conditioned with current-transporting ionic species.
Attempts to reduce the conditioning time in situ meet with problems. The application of high voltages in order to force the conditioning process often results in damage to the membrane, especially those membranes the surfaces of which are tightly cross-linked. While heat speeds the conditioning process, the application of heat within a commercial cell requires additional equipment. High strength alkali metal hydroxide solutions work to advantage but are detrimental to the dimensionally stable anodes routinely employed. Such solutions also initially cause dehydration of the membrane to occur, again resulting in a change in dimension.